The present invention relates to mirrors used for inspection and examination. More specifically, the invention relates to a dental optical mirror element to be used in combination with a handle and a light source.
Hand held dental mirrors have long been used in the field of dentistry and are well known to those skilled in the art. Dental mirrors are used to view areas of the mouth which are not easily viewable by direct line of sight.
Dental mirrors have been combined with a light source. Combining a dental mirror with a light source greatly increases the ability to view relatively dark areas of the mouth which are not visible by direct line of sight. Examples of such mirrors are disclosed in U.S. Pat. Nos. 1,747,009 to Jordan; 2,428,975 to Lamb; 3,638,013 to Keller; 5,139,421 to Verderber; 5,457,611 to Verderber; 6,443,729 to Watson; 6,702,577 to Wong and 7,066,734 to Cooper.
The illuminated dental mirror disclosed in U.S. Pat. No. 5,139,421 to Verderber is known to be the most successful illuminated mirror marketed to dentists. The Verderber mirror was long produced and marketed by Welch-Allyn, Inc., of Skaneateles, N.Y. and is currently produced and marketed by Integra LifeSciences Holdings Corporation's Miltex Dental business of York, Pa.
In U.S. Pat. No. 5,139,421 Verderber discloses a mirror element including a light transmitting shank. While the Verderber mirror has demonstrated commercial success, it is problematic; being relatively expensive to manufacture and relatively inefficient in terms of light transmission.
The shank of the Verderber mirror must be relatively thick in order to admit adequate light and transmit adequate light. As for example, the Verderber mirror is manufactured with a shank diameter of 0.25 inches. It has been discovered that a shank of this diameter is prone to gas bubble inclusions: after molten plastic is injected into a mold, the surface of the cylindrical shank hardens first. As the still molten plastic material within the shank cools, it shrinks, creating gas bubble inclusions. Gas bubble inclusions within the shank are a major fault as they interfere with light transmission and significantly reduce the efficiency of the instrument. To reduce the incidence of gas bubble inclusions within the shank of the Verderber mirror element, high mold pressure must be maintained and the shank must be cooled slowly. Operating an injection mold at high pressure reduces the life of the mold. Cooling the mold slowly increases the molding cycle time. Relatively short mold life and relatively slow molding cycles contribute significantly to the cost of manufacturing the Verderber mirror. It would be ideal to provide an optical mirror element having high quality light distribution, but which could be molded using low mold pressure and fast molding cycles.
The volume of plastic material comprising the shank of the Verderber mirror element accounts for about two thirds of the plastic material in the mirror element and is significant in terms of materials cost. Reducing the volume of plastic material comprising the shank of the Verderber mirror element would result in a considerable reduction in part cost. It would be ideal to provide a mirror element using a relatively small volume of plastic material, thereby significantly reducing the cost to produce said mirror element.
Some volume of light traveling through the shank of the Verderber mirror is lost as a result of interference with micro-bubbles and inclusions. As discussed in greater detail above, the Verderber shank is prone to gas bubble inclusions. Although high mold pressure and relatively slow molding cycles reduce the incidence of major gas bubbles, micro-bubbles are inevitably present within said shank. Further, inclusions of dust, oils and other unknown materials are inevitably present within said shank. A portion of the light transmitted through the shank strikes these inclusions and is thereby scattered, reducing the efficiency of the instrument. It would be ideal to provide a mirror element in which the distance light is transmitted through molded optical plastic is minimized.